The present invention relates to a gas turbine combustor and a gas turbine and, more particularly to a gas turbine combustor which is able to effect both of premixed combustion and diffusion combustion.
Conventional burners of various constructions are proposed for use in gas turbine combustors. An example of those burners is disclosed in JP A 1-137117 in which a diffusion pilot section of a fuel feed pipe and an air feed pipe arranged coaxially is provided in the center of a premixing chamber. U.S. Pat. No. 4,463,568 discloses a proposal in which various kinds of fuel are available, a baffle plate is arranged at an outlet of a supply pipe for mixture gas of fuel and gas, and an air supply pipe is arranged in an outer periphery thereof for a gas flow to spread toward the outer peripheral portion. JP A 59-101551 discloses a proposal in which a premixing chamber of fuel and air and an air supply pipe for a diffusion pilot burner are common, only air is flowed into the premixing chamber according to load. Further, an example of conventional stabilizers is disclosed in JP A 57-115624 in which a small wing is mounted on a V-shaped stabilizer (V gutter) to make better mixing in accompanying flows in the wake of the V gutter. Further, JP A 1-210721 proposes a method of mounting of a stabilizer having a generally V-shaped cross-section. Still further, U.S. Pat. No. 3,736,746 discloses a proposal concerning an arrangement position of a stabilizer.
For gas turbines, it is necessary to be operated under a wide output range corresponding to a large load change from start up to a rated load. Therefore, one of essential factors for the gas turbines is stable combustion and no occurrence of misfire even if operational conditions such as air flow rate, fuel flow rate, etc. change largely from the starting to the rated load.
On the other hand, a combustion method in which NOx production is suppressed is desired strongly for gas turbine combustors in order to reduce emission of NOx from the gas turbine combustors. Premixed combustion that fuel and air are premixed and then subjected to combustion can realize low NOx emission, so that use of the premixed combustion increases in order to comply with a demand of low NOx emission which is increasing more and more recently. However, in general, the premixed combustion is narrow stable combustion range and easy to fall into misfire as compared with diffusion combustion in which fuel and air are burnt while they are being mixed. Therefore, in order to reduce NOx emission while keeping combustion stable, it is necessary to combine effectively the diffusion combustion and the premixed combustion.
For gas turbine combustors, a fuel air ratio (fuel flow rate (kg/sec)/air flow rate (kg/sec)) which is weight ratio between fuel flow rate supplied into the combustor and air flow rate from a compressor is a important factor of combustion stability. Of misfire, there are two cases, in one case of which flame is blown out when fuel air ratio is small or air flow velocity is fast, and in another case, fuel air ratio is large and flame is blown out by floating up of the flame or combustion vibrations.
In gas turbine combustors, a fuel air ratio of the entire combustor changes from about 0 at time of starting to about 0.028 at the rated load including air for cooling which also flows into the combustor. However, the air for cooling flowing into the combustor is small around the burner and only air may be supplied from a burner not served burning under some operational conditions, so that it should be considered that a partial fuel air ratio of the burner serving the combustion becomes 0.05 or more in maximum.
The above-mentioned any conventional technique does not take sufficiently into consideration forming clearly flame stabilization region or zone in such a wide range of fuel air ratio, particularly, flame stabilization when fuel flow rate is small at such time as start up time, speed increasing time or low load operation time. Further the technique does not touch flame stabilization while reducing NOx emission under operational conditions that fuel flow rate is large.